1. Field of the Invention
The present invention relates to a viscous and rubber-type torsional damper to dampen torsional oscillations or vibrations of rotary masses such as engine crankshafts or the like.
2. Description of the Prior Art
Conventional torsional dampers are generally classified into a rubber-type damper typical examples of which are shown in FIGS. 4 and 5, a viscous and rubber-type damper shown in FIG. 6, and a viscous-type damper shown in FIG. 7. Rubber-type dampers are further classified into a pulley-type damper shown in FIG. 4 and a disk-type damper shown in FIG. 5.
The pulley-type, rubber-type damper 60 of FIG. 4 has an advantage that the diametrical size of the damper is comparatively small as the pulley portion 62 is also used as a damping mass, but has the disadvantage that the damping ability is not great. The disk-type, rubber-type damper 64 of FIG. 5 has an advantage that the damper has a comparatively great damping ability because the inertial mass 66 is designed to be large, but has a disadvantage that the diametrical size of the damper is too great. The conventional viscous and rubber-type damper 68 of FIG. 6 has an advantage that the damping ability is great due to the rubber damping and the fluid viscous damping, but has disadvantages in that the diametrical size of the damper is too great, as it is in to the disk-type damper, since the radially extending surfaces 70 and 72 are used as working surfaces for generating a shear force in the viscous fluid and the number of the constructing members is increased because a seal member 74 needs to be provided. The viscous-type damper 76 of FIG. 7 has an advantage that the damping characteristic at high speeds is excellent, but has a disadvantage that the damping ability at low speeds is small.